Radio apparatus employing slot antenna



June 1951 N. HARVEY 2,555,443

RADIO APPARATUS EMPLOYING SLOT ANTENNA Filed June 8, 1948 MODULATOR INVEN TOR. E Z Norman L. Harvey BY fliiorney Patented June 5, 1951 Norman Lrlial'vey, Huntington Station,-N. Y.., assignor to 'Sylvania Electric Products Inc., a corporation of Massachusetts Applicationluneil, 1948,; Serial No. 31;722

'Claims. l n This invention relates to high-frequencyradlo apparatus, employing an antenna.

-Slotantennas have been widely used inrecent years, in which the antenna takes the form. of a sheet having along and narrow slot, with the slot coupled to a radio signal generatoror a, receiver. The slot antenna is notable for its effectiveness over a broad frequency range, making it Well-suited to transmitters operating over a broad band of frequencies such as-pulse-transmitters, frequency-modulation transmitters, and for broad-band receivers. as well. Where the antenna is of sheet-.metaLgenerally cylindrical in form and having a single half-wavelengthvlongitudinal slot,. a broad radiation pattern is obtained. This is useful particularly for maintaining communication between airborne and ground units, wherethe relative .orientation of the units is subject to continuous change. Directional cylindrical slot antennas can also be constructed by. attention to length and number of; slots.

Radio units incorporating a. slot antenna, including both receivers and transmitters of various within the hollow of a cylindrical antenna and eliminating the transmission line. The several aspects. of the invention, together with further features of'novelty, willbe better appreciated from the following detailed disclosure of a specific, illustrative embodiment of the invention, shown in the accompanying drawings in which:

Fig. 1 is a somewhat diagrammatic view of one form of slot antenna-enclosing a radio unit to forms, commonly emplo an impedance in the stage coupled to the antenna which is required to be. high over the operating frequency range while the antenna is required to. have a radiation impedance of only a few hundred ohms. .I have succeeded in eliminating that stage impedance as a distinct structure by utilizing the edges of the slot in the antenna as the impedance. This has the further effect of imparting to the directly coupled portion of the radio unit thesame broad frequency characteristic for which the-slot antenna is noted. The desiredmatching of impedances of the antenna'a-nd th -coupled stage is effected by correct proportioning of the slot-and by coupling the stage atthe proper pointbetween one end and centerof theslot. There .is the further result that the matching network ordinarily used between the antenna and the. unit is also eliminated. .In particular, where the-slot is utilizedin an anode circuit .as the: principal frequency-determining unit of .an oscillator,-.the resulting transmitter is especially well-suitedto forms of radio signallingrequiring broad frequency bands, as to pulse-communication and to frequency modulation about thecenter'frequency of the slot edges which then actsomewhat as Lecher wires having shorted terminals,

The usual transmission line between an antenna and the coupled radio unit involves troublesome problems of shielding and design. These I have overcome pursuant to another aspect of the invention by enclosing the radio unit bodily which theslot is connected; and

Fig. 2 is the wiring diagram of an amplitudemodulated oscillator coupled to the slot antenna of Fig. 1.

In Fig. 1 cylinder I0 is provided with a longitudinal slot 12 to constitute a cylindrical slot antenna. Cylinder I0 is closed by metal ends l4, although this is not-entirely necessary. In the embodiment of Fig. 1 slot I2 is provided with transverse end portions l6 which have the effect of adapting the slot to lower-frequency operation than a similar slot l2 withoutsuch extensions. Translator l8 that may bea receiver or a signal generator is enclosed within cylindrical antenna I 0 and is coupled to that antenna by short leads" 20 that :are joined to opposite edges .of the slot. Unit l8 advantageously is batteryoperated and in this respectis entirely enclosed within antenna ID. This eliminates the need for .a transmission line thatwould ordinarily be used between, unit 18 and. its antenna, and, avoidsthe shielding and matching difiiculties connected with transmission lines in uses of that kind.

The foregoing. apparatus represents a compact and lightweight radio complete in itself, which is well suited to airborne communication because of its broad radiation pattern and its wide-band frequency characteristic. Unit I8 of Fig. 1 advantageously takes the form of a modulated oscillator, particularly an amplitude-modulated oscillator as shown in Fig; 2. This illustrative oscillator'has a push-pull pair of triodes 22 and' 24, the grids of'which arebiased by grid-leak resistor 2B and capacitor 28, which are cross-coupled to the anodes of the opposite triodes by capacitorstn and 32. The anodes of triodes 22 and 24-are energized through a center-tapped high-frequency-chokeB by the positive terminal of the direct-current supply that is bypassed by capacitor 36. Modulator 31, which injects varying voltage into the grid circuit, is coupled to the grids in parallel through coupling capacitor 38 and center-tapped radio frequency choke 40,

The principal element of the oscillator that determines its center frequency would usually be a ooil-and-capacitor combination or comparable resonator forming an integral part of the oscillator and coupled to the antenna through a carefully designed transmission line. In the present apparatus the oscillator utilizes the slotted antenna itself as the principal tuned impedance for determination of the center operating frequency. The anodes of tubes 22 and 24 are coupled through capacitors 42 and 44 through leads 20 to the opposite edges of slot 12 of antenna l9. Antenna has the proper low impedance, of the order of a few hundred ohms, for effective radiation. The edges of the slot are effective, somewhat as the parallel wires of a Lecher system, to present to the oscillator the high impedance required by vacuum tubes 22, 24 for their efficient operation. The exact impedance presented by the slot to the oscillator depends on various factors, such as the separation of the edges of the slot and the point along the slot (measured from the center toward one of the ends I6) at which leads 20 are connected.

It will thus be apparent that the anode tuned impedance or tank circuit as a distinct element has been eliminated together with the usual matching line between the oscillator and the antenna. Where the slot is utilized both as the means for exciting the antenna and as the primary frequency control of the oscillator, that oscillator can be very efiectively modulated to yield frequency components that requires the broad-band characteristic of the antenna. Furthermore, because the oscillator utilizes the slot as its tank circuit, it can be mounted adjacent, and within, the cylindrical antenna. With this arrangement a compact, lightweight, and aerodynamically suitable transmitter is provided, with improved characteristics as already stated. By filling the slot with insulating material such as polystyrene, smoothed flush with the external surface of the antenna, the aerodynamic characteristics of the antenna can be improved.

Varied modifications and applications of the novel aspects of the foregoing disclosure will occur to those skilled in the art; and it is therefore fitting that the appended claims be given broad interpretation, consistent with the spirit and scope of the invention.

What is claimed is:

1. An oscillator capable of operation over a broad frequency range comprising an electrondischarge device having a grid, a cathode and an anode, and a metal sheet having a slot one of the edges of which is connected to said anode to serve both as a tank circuit and for propagation of the oscillations generated.

2. Radio apparatus comprising electron-discharge means, a hollow slot antenna enclosing said electron-discharge means, and a direct connection between electrodes of said electron-discharge means and said slot antenna such that the edges of the slot constitute the principal tuned impedance between said device and said antenna.

3. A radio transmitter comprising a signal generator including an electron-discharge device having an anode, a slotted antenna, the slot edges of said antenna being directly connected to said device in a manner to function as the anode tuned impedance of said device.

4. Radio apparatus comprising a cylindrical antenna having a longitudinal slot, electron-discharge means enclosed within said cylindrical antenna, and direct connections between electrodes of said electron-discharge means and opposite edges of said slot.

5. A radio transmitter comprising a cylindrical antenna having a longitudinal slot, a signal generator enclosed in said cylindrical antenna and including electron-discharge means, and direct connections between electrodes of said electrondischarge means and opposite edges of said-slot.

6. A radio transmitter comprising an oscillator, a cylindrical antenna having a longitudinal slot, said oscillator including electron-discharge means having electrodes directly connected to the edges of said slot.

'7. Radio apparatus comprising a cylindrical slot antenna, an oscillator enclosed in said antenna, and a modulator for producing a range of frequency components in the output of said oscillator, said oscillator including electron-dis charge means having electrodes directly connected to the edges of said slot.

8. Radio apparatus comprising electron-discharge means, a slot antenna, and direct connections between electrodes of said electron-discharge means and the edges of the slot of said antenna such that said edges constitute a coupling to the antenna and such that said edges also constitute a parallel-line resonator that tunes said electron-discharge means.

9. A radio transmitter comprising an oscillator including an electron-discharge means, a cylindrical antenna having longitudinal slot, and direct connections between electrodes of said electron-discharge means and edges of said slot, the slot edges thereby constituting not only the coupling to the antenna, but additionally the tuned output impedance of said oscillator.

10. A radio transmitter comprising a signal generator including electron-discharge means, a cylindrical antenna enclosing said means, said antenna having a longitudinal slot, and direct connections between electrodes of said device and the edges of said slot, which slot edges thereby couple said signal generator to said antenna and tune said electron-discharge means.

NORMAN L. HARVEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,125,969 Turner Aug. 9, 1938 2,129,852 Leib Sept. 13, 1938 2,190,712 Hansen Feb. 20, 1940 2,234,293 Usselman Mar. 11, 1941 2,241,119 Dallenbach May 6, 1941 2,404,745 Roberts July 23, 1946 2,414,266 Lindenblad Jan. 14, 1947 2,415,094 Hansen et a1 Feb. 4, 1947 OTHER REFERENCES Pylon Antenna, FM & Television, September 1946. Pages to 47. 

